The present invention generally relates to vehicle stability control and more particularly relates to a method and a device for establishing a value, especially a momentum, produced externally, driving or braking a vehicle.
The longitudinal dynamics of a vehiclexe2x80x94speed and accelerationxe2x80x94is influenced by various internal and external values, especially momentums. Within the meaning of this description, internal values/momentums are the motor torque, the brake torque or the normal resistance (which can be described internally by tables based on pragmatic values or by constants or formulas considering the motional status of the vehicle in connection with the characteristics/parameters of the vehicle). These values can be established in a relatively precise manner by various measures so that it is possible to consider their influence on the longitudinal dynamics. Additionally there are also externally produced values resulting particularly variable in addition to the normal resistance described above (which can be described internally). This includes, e.g. the slope descending force when a vehicle is driving on an inclined road. This slope descending force leads to a momentum which influences the longitudinal dynamics of the vehicle. The same applies for wind forces, extraordinary rolling resistances or similar. It is not possible (or only with difficulties) to establish these externally produced values with traditional sensors, so that usually additional sensors are required which have to be eliminated.
However, for some applications it is desirable to know also externally produced values driving or braking a vehicle, especially momentums. An example for such an application would be a starting aid when driving up a hill. Such starting aids shall facilitate the complicated handling of brake, parking brake, clutch and motor. At the same time it has to be assured that the vehicle never rolls back, in order do avoid e.g. collisions with vehicles being parked in downhill direction. If a vehicle shall be started driving up the hill, the rules described schematically in FIG. 4 apply in a first approximation. The weight FG of the vehicle can be decomposed into a normal component FN and a tangential component FT on the wheel of a one-wheel model. Together with the wheel radius rR, FT leads to a slope descending momentum MH according to the formula:
MH=FGxc2x7sin xcex1xc2x7rR
In this case xcex1 is the angle of inclination. Without further intervention the slope descending momentum MH would cause the vehicle to run down the hill. The brake torque MB and the motor torque MM introduced during the start of the vehicle, counteract against this momentum. An aid for starting up the hill can influence, e.g. the brake torque MB. But the influence has to be such to assure at all times that the inequation
MH less than MB+MM
is complied with because only in this case the vehicle is definitely prevented from rolling back. In order to satisfy the equation mentioned above, the slope descending moment has to be known.
Similar considerations as above apply in dynamic situations (vehicle speed unlike zero). When driving slowly up the hill in urban traffic, the considerations mentioned above could become an important factor. Also in such cases it is desirable to know the values produced externally and driving or braking a vehicle, especially momentums, in order to influence the vehicle in an adequate manner.
From U.S. Pat. No. 5,455,767 a control for a vehicle drive with an automatic gear is known which determines a correction term by comparing an estimated and a measured output speed representing a basic value for the inclination angle. On the input side a motor torque and a resistance momentum of the vehicle are delivered to a time element. The difference between the estimated and the measured output speed is countercoupled to the rotation angle acceleration.
It is the object of the present invention to indicate a method and a device for establishing an externally produced value, especially such a momentum, which drives and brakes the vehicle.
The externally produced values, and in particular the momentums, are determined by an observer. The observer receives internally produced values, especially momentums, which drive or brake the vehicle, establishes, how the longitudinal dynamics of the vehicle should develop, compares this result with the measured values of the longitudinal dynamics and concludes from possible deviations that there are externally produced values, especially momentums, driving or braking a vehicle.